Lasers or X-rays: 7 Key Differences of Handheld LIBS vs XRF

The Rolling Stones or The Beatles? Spiderman or Batman? iPhone or Android?

Is there a winner in each of these classic match-ups? Maybe.

What we know for sure, though, is there are differences. There’s a time and place for the Stones, just as there’s a time and place for Paul, John, George, and Ringo.

The same goes for the handheld Laser-Induced Breakdown Spectrometer (LIBS) and handheld X-ray Fluorescence (XRF). Yes, both technologies are used for positive material identification (PMI). But, in certain circumstances, one is better to use over the other. You have to be familiar with the strengths and weaknesses of each.

That’s exactly what I intend to discuss in this article: the differences between LIBS and XRF for PMI.

So, what are the differences between handheld LIBS versus XRF? The differences between LIBS vs. XRF include:

1. History & reputation
2. Agility & ease of use
3. Precision & accuracy
4. Ability to test light elements
5. Speed
6. Safety
7. Cost of ownership

Let’s take a closer look at these 7 differences.

Psst: This post is based on a podcast with co-host Chris Carolan. To hear this episode (and more like it), subscribe to The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.

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LIBS vs. XRF: How they work

Before we get into the specific differences between LIBS and XRF, it’s important to understand how each technology works.

How LIBS works

Laser-induced breakdown spectroscopy (LIBS) uses a laser-source to burn the metal sample, vaporizing a small portion of it. This, in turn, excites the atoms within the metal alloy, causing light to be emitted.

Based on the light signatures being released, the analyzer can identify the elements and concentrations.

Then, the identified elements can be compared with a library of grades to provide an alloy grade identification. (Ex. Al 6063)

Here’s how LIBS works step-by-step:

1. The laser-source burns the metal, vaporizing the atoms within the sample.
2. This generates a light signature based on the energies the atoms are giving off.
3. The detector collects the light signature.
4. The analyzer, then, is able to determine the chemistry and composition of the metal sample.
5. Lastly, the analyzer compares the percentages, chemistry, and composition of the sample to a grade library to identify the alloy.

Basic LIBS Diagram

LIBS can now do the same thing that XRF is doing in most applications, just using a laser source instead of radiation.

How XRF works

X-ray fluorescence (XRF) uses radiation to excite the atoms of the metal sample.

Each atom, then, emits a signature energy that corresponds with its element. The XRF instrument detects the energies and generates a virtually complete chemistry of the metal.

The following steps detail more specifically how XRF tests metals.

1. Primary X-rays are generated by the source and permeate the surface of the metal sample.
2. The primary X-ray strikes atoms within the sample, creating secondary X-ray beams.
3. An electron (aka, negatively-charged particle) is cast out from each affected atom, creating a vacancy around each atom. This makes the atom unstable.
4. In order to regain stability, an electron from a higher up energy level fills the vacancy. A secondary X-ray is produced from the electron moving between two energy levels.
5. The secondary X-ray is specific to the present element.
6. The secondary X-ray beams are collected by the detector and processed by the analyzer. A spectrum is generated, revealing each X-ray beam’s peak intensity compared to its energy.
7. The analyzer identifies the element from the peak energy.
8. Lastly, the analyzer calculates the elemental composition of the metal and compares it to a grade library to provide alloy identification. (Ex. SS 316)

Atomic view of how XRF works

All in all, both LIBS and XRF are going to provide grade identification and chemistry of the alloy. That might be where the similarities end. Let's get into the differences.

1. LIBS vs. XRF: History & Reputation

There are several key differences in the histories and reputations of LIBS and XRF technologies.

LIBS history and reputation

Although LIBS technology has been around for nearly 50 years, the handheld LIBS is only 7 or 8 years old.

We can thank the advancement in laser technology for the handheld LIBS. The device used to only come in benchtop form, a rather big and bulky apparatus. It was practically impossible to move the benchtop LIBS from the lab out into the field.

Now, thanks to the miniaturization of lasers, LIBS can be taken to the same places XRF has been going for many years.

The thing about LIBS, however, is there is a lot less education and training around using it for PMI.

The first versions of the handheld LIBS — not unlike most new technologies — did not perform up to expectations (or, rather, promises made by suppliers).

Now that the kinks have been ironed out, the handheld LIBS is an exceptional tool for identifying materials. Unfortunately, many misconceptions still exist throughout the metals industry about its performance and usability.

XRF history and reputation

X-ray fluorescence technology has been around for over 70 years in one form or another. It started out much like how LIBS began: in benchtop, “go-ahead-and-try-to-move-me” form.

First created by Niton in 1994, the handheld XRF has been a tried-and-true device for PMI testing.

Since it’s been around for 25 years, the handheld XRF is widely accepted and used for metal testing. Though it’s a popular form of PMI, XRF is regulated by most states and countries because of its use of radiation.

2. LIBS vs. XRF: Agility & Ease of Use

When you get right down to it, out of its box, the handheld XRF tends to be easier to use than the handheld LIBS. Yet, with proper training, there is almost no gap between the two technologies for ease of use.

Using handheld LIBS

Handheld LIBS instruments are portable and easily moved from place to place.

In order to produce the best results with handheld LIBS, the device needs complete contact with the sample. This is because the light being emitted needs to be 100% detectable and will escape easily without perfect contact. If you don't see all of the light emissions, you can't be sure you are seeing a quality result.

To get a clean burn with handheld LIBS, more training needs to be involved than there would be with handheld XRF. Nevertheless, once properly trained, the handler should be able to produce results similar to those of an XRF instrument. In many cases, better results are seen in applications including light elements like magnesium and aluminum.

Once you have LIBS training, it behaves very similarly to XRF and can serve in many of the same applications regarding metal identification.

 

Using handheld XRF

The handheld XRF instrument is also a very portable tool for PMI testing. However, a less rugged design with expensive, fragile parts does call for a bit more care in handling the equipment.

Handheld XRF devices have been regarded as point-and-shoot. While handheld XRF is more forgiving than LIBS in terms of direct contact with the sample and cleanliness of the sample, the user oftentimes doesn’t understand how the results are being generated.

This lack of understanding can lead to inconsistencies and lack of quality in PMI testing.

3. LIBS vs. XRF: Precision & Accuracy

Handheld XRF tends to yield more precise results than LIBS. With the right training, both LIBS and XRF provide accurate PMI testing.

It’s best to use handheld XRF when…

• You need to report to more than 2 decimal places.
• You need to detect trace levels of an element (<0.1%).
• You need to identify for heavier alloys, such as tungsten alloys. (Tungsten is too tough for LIBS to vaporize and get a good light signal.)

While handheld XRF can test for a wider variety of elements, LIBS is better for testing lighter elements. This brings us to the fourth main difference between XRF and LIBS.

4. LIBS vs. XRF: Ability to Test for Light Elements

When it comes to light elements, such as

• Aluminum (Al),
• Beryllium (Be),
• Carbon (C),
• Lithium (Li),
• Magnesium (Mg),
• Silicon (Si),

handheld LIBS should be your tool of choice. LIBS allows you to see those lighter elements more easily than XRF can. (Note: handheld XRF cannot detect Be, C, or Li)

5. LIBS vs. XRF: Speed

Handheld LIBS is faster than XRF at testing.

LIBS test speed

A handheld LIBS device can test a sample in as little as 1-3 seconds. That’s as long as the sample surface is adequately cleaned and there’s direct contact between the tool and the metal.

XRF test speed

The speed at which a handheld XRF tool can test a sample depends on the handler and what they are testing. Different test results can be generated if one user gives the device 5 seconds to test as opposed to 10 or 15 seconds.

Overall, handheld XRF speeds can vary between 3 and 30 seconds depending on the material and elements of interest.

6. LIBS vs. XRF: Safety

LIBS is a far safer method of PMI than XRF.

LIBS safety

When using handheld LIBS, special protective eye wear is recommended. Otherwise, there aren’t any other imperative safety concerns. With proper training, you do not need protective eye wear.

XRF safety

Because XRF uses radiation to analyze the composition of metals, it can be quite harmful if not used correctly.

A few things to remember when using handheld XRF:

• Even though you can’t see anything, there’s radiation exuding from a handheld XRF device.
• If the XRF device is not handled properly, you run the risk of exposing others to the open beam of radiation.
• Do not hold samples in your hand — radiation can be transmitted through the sample into your hand.
• Most states regulate the use of XRF. Make sure you know the rules pertaining to using handheld XRF.

7. LIBS vs. XRF: Cost of Ownership

Upfront, the cost of a handheld XRF device can be less than a handheld LIBS tool. However, the ongoing maintenance costs of handheld XRF surpasses the total cost of handheld LIBS.

LIBS cost of ownership

The initial cost of a new handheld LIBS instrument runs from $20k-$40k. The range in cost is due to the fact that some LIBS tools can test for carbon and some cannot.

Aside from the initial cost, LIBS cost of ownership is very minimal, especially compared to the cost of owning a handheld XRF analyzer.

Because it’s made for the field and sturdier than other PMI testing devices, the laser source is the only thing you’ll need to worry about repairing or replacing on a handheld LIBS instrument. Laser source repairs or replacements cost $3,500 max, but oftentimes don’t even cost that much and may not even be needed while you own the analyzer.

Considering its relatively low lifetime cost, handheld LIBS is generally the most cost-effective method of PMI testing.

XRF cost of ownership

Purchasing a new handheld XRF analyzer will put you anywhere between $15,000 and $40,000. Costs will vary depending on the quality, performance, and functionality of the tool.

Though initial costs of handheld XRF technology can be than LIBS, the ownership costs can pile up quickly.

Handheld XRF is a more fragile technology for PMI testing. Many parts on the inside of the device are prone to breaking, such as the delicate X-ray tubes and detectors. X-ray tube or detector replacement runs $7,000-$10,000.

Note: The environments in which handheld XRF and LIBS are normally used aren’t very forgiving. In many cases, it’s easy to drop or bump whichever handheld device you’re using for PMI. This can mean the end of many handheld XRF devices used out there today.

LIBS vs. XRF Takeaways

To wrap up, there are three main points I hope you walk away from this article with:

1. XRF is a tried-and-true method of PMI and can get the job done in most cases.
2. LIBS is a viable alternative in many situations of PMI and is actually more suitable for testing light elements which is needed for aluminum alloy identification.
3. Although LIBS takes some training (particularly to break XRF habits), it’s a faster, safer, and more cost-efficient way to test metals.

Until next time, Never Stop Testing Your Metal.

Want to learn more about positive material identification? Check out The Manufacturing Show on Apple Podcasts, Spotify, or wherever you listen to podcasts.